First off the bat a misfire and he was beaten to a pile of sludge by the target.
Wouldn't you have to cart around a massive compressed air canister with that? I guess you could probably get away with a paintball compressed air system, but with the gun alone being around £250ish....you can get a simple enough shotgun for similar money. Or a pretty good bow, or crossbow, or air rifle...I think it may well be an option, but there are many others that I'd go for first.
Impressive YL in the second clip Morty!
If I tried that I'd be asking the local hospital to see if they could sew back on the digits stuck in the chamber of the gun :-(